The frozen neoplasms from mice exposed to chloroprene were examined for p53 protein by immunohistochemical method. The neoplasms with positive p53 protein were evaluated by PCR-based assays, including SSCP and direct sequencing analysis. Two second exon CGA mutations were identified, one in H-ras and one in K-ras. No other transforming genes were detected in total 12 multi-site neoplasms. Further molecular mechanistic studies on chloroprene-induced neoplasms in this mouse model may faciliatate understanding potential carcinogenic risks of chloroprene to humans.